mirror of
https://github.com/rails/rails.git
synced 2022-11-09 12:12:34 -05:00
438 lines
13 KiB
Markdown
438 lines
13 KiB
Markdown
The Basics of Creating Rails Plugins
|
||
====================================
|
||
|
||
A Rails plugin is either an extension or a modification of the core framework. Plugins provide:
|
||
|
||
* a way for developers to share bleeding-edge ideas without hurting the stable code base
|
||
* a segmented architecture so that units of code can be fixed or updated on their own release schedule
|
||
* an outlet for the core developers so that they don’t have to include every cool new feature under the sun
|
||
|
||
After reading this guide you should be familiar with:
|
||
|
||
* Creating a plugin from scratch
|
||
* Writing and running tests for the plugin
|
||
|
||
This guide describes how to build a test-driven plugin that will:
|
||
|
||
* Extend core Ruby classes like Hash and String
|
||
* Add methods to ActiveRecord::Base in the tradition of the 'acts_as' plugins
|
||
* Give you information about where to put generators in your plugin.
|
||
|
||
For the purpose of this guide pretend for a moment that you are an avid bird watcher.
|
||
Your favorite bird is the Yaffle, and you want to create a plugin that allows other developers to share in the Yaffle
|
||
goodness.
|
||
|
||
--------------------------------------------------------------------------------
|
||
|
||
Setup
|
||
-----
|
||
|
||
_"vendored plugins"_ were available in previous versions of Rails, but they are deprecated in
|
||
Rails 3.2, and will not be available in the future.
|
||
|
||
Currently, Rails plugins are built as gems, _gemified plugins_. They can be shared across
|
||
different rails applications using RubyGems and Bundler if desired.
|
||
|
||
### Generate a gemified plugin.
|
||
|
||
|
||
Rails 3.1 ships with a `rails plugin new` command which creates a
|
||
skeleton for developing any kind of Rails extension with the ability
|
||
to run integration tests using a dummy Rails application. See usage
|
||
and options by asking for help:
|
||
|
||
```bash
|
||
$ rails plugin --help
|
||
```
|
||
|
||
Testing your newly generated plugin
|
||
-----------------------------------
|
||
|
||
You can navigate to the directory that contains the plugin, run the `bundle install` command
|
||
and run the one generated test using the `rake` command.
|
||
|
||
You should see:
|
||
|
||
```bash
|
||
2 tests, 2 assertions, 0 failures, 0 errors, 0 skips
|
||
```
|
||
|
||
This will tell you that everything got generated properly and you are ready to start adding functionality.
|
||
|
||
Extending Core Classes
|
||
----------------------
|
||
|
||
This section will explain how to add a method to String that will be available anywhere in your rails application.
|
||
|
||
In this example you will add a method to String named `to_squawk`. To begin, create a new test file with a few assertions:
|
||
|
||
```ruby
|
||
# yaffle/test/core_ext_test.rb
|
||
|
||
require 'test_helper'
|
||
|
||
class CoreExtTest < Test::Unit::TestCase
|
||
def test_to_squawk_prepends_the_word_squawk
|
||
assert_equal "squawk! Hello World", "Hello World".to_squawk
|
||
end
|
||
end
|
||
```
|
||
|
||
Run `rake` to run the test. This test should fail because we haven't implemented the `to_squawk` method:
|
||
|
||
```bash
|
||
1) Error:
|
||
test_to_squawk_prepends_the_word_squawk(CoreExtTest):
|
||
NoMethodError: undefined method `to_squawk' for [Hello World](String)
|
||
test/core_ext_test.rb:5:in `test_to_squawk_prepends_the_word_squawk'
|
||
```
|
||
|
||
Great - now you are ready to start development.
|
||
|
||
Then in `lib/yaffle.rb` require `lib/core_ext`:
|
||
|
||
```ruby
|
||
# yaffle/lib/yaffle.rb
|
||
|
||
require "yaffle/core_ext"
|
||
|
||
module Yaffle
|
||
end
|
||
```
|
||
|
||
Finally, create the `core_ext.rb` file and add the `to_squawk` method:
|
||
|
||
```ruby
|
||
# yaffle/lib/yaffle/core_ext.rb
|
||
|
||
String.class_eval do
|
||
def to_squawk
|
||
"squawk! #{self}".strip
|
||
end
|
||
end
|
||
```
|
||
|
||
To test that your method does what it says it does, run the unit tests with `rake` from your plugin directory.
|
||
|
||
```bash
|
||
3 tests, 3 assertions, 0 failures, 0 errors, 0 skips
|
||
```
|
||
|
||
To see this in action, change to the test/dummy directory, fire up a console and start squawking:
|
||
|
||
```bash
|
||
$ rails console
|
||
>> "Hello World".to_squawk
|
||
=> "squawk! Hello World"
|
||
```
|
||
|
||
Add an "acts_as" Method to Active Record
|
||
----------------------------------------
|
||
|
||
A common pattern in plugins is to add a method called 'acts_as_something' to models. In this case, you
|
||
want to write a method called 'acts_as_yaffle' that adds a 'squawk' method to your Active Record models.
|
||
|
||
To begin, set up your files so that you have:
|
||
|
||
```ruby
|
||
# yaffle/test/acts_as_yaffle_test.rb
|
||
|
||
require 'test_helper'
|
||
|
||
class ActsAsYaffleTest < Test::Unit::TestCase
|
||
end
|
||
```
|
||
|
||
```ruby
|
||
# yaffle/lib/yaffle.rb
|
||
|
||
require "yaffle/core_ext"
|
||
require 'yaffle/acts_as_yaffle'
|
||
|
||
module Yaffle
|
||
end
|
||
```
|
||
|
||
```ruby
|
||
# yaffle/lib/yaffle/acts_as_yaffle.rb
|
||
|
||
module Yaffle
|
||
module ActsAsYaffle
|
||
# your code will go here
|
||
end
|
||
end
|
||
```
|
||
|
||
### Add a Class Method
|
||
|
||
This plugin will expect that you've added a method to your model named 'last_squawk'. However, the
|
||
plugin users might have already defined a method on their model named 'last_squawk' that they use
|
||
for something else. This plugin will allow the name to be changed by adding a class method called 'yaffle_text_field'.
|
||
|
||
To start out, write a failing test that shows the behavior you'd like:
|
||
|
||
```ruby
|
||
# yaffle/test/acts_as_yaffle_test.rb
|
||
|
||
require 'test_helper'
|
||
|
||
class ActsAsYaffleTest < Test::Unit::TestCase
|
||
|
||
def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
|
||
assert_equal "last_squawk", Hickwall.yaffle_text_field
|
||
end
|
||
|
||
def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
|
||
assert_equal "last_tweet", Wickwall.yaffle_text_field
|
||
end
|
||
|
||
end
|
||
```
|
||
|
||
When you run `rake`, you should see the following:
|
||
|
||
```
|
||
1) Error:
|
||
test_a_hickwalls_yaffle_text_field_should_be_last_squawk(ActsAsYaffleTest):
|
||
NameError: uninitialized constant ActsAsYaffleTest::Hickwall
|
||
test/acts_as_yaffle_test.rb:6:in `test_a_hickwalls_yaffle_text_field_should_be_last_squawk'
|
||
|
||
2) Error:
|
||
test_a_wickwalls_yaffle_text_field_should_be_last_tweet(ActsAsYaffleTest):
|
||
NameError: uninitialized constant ActsAsYaffleTest::Wickwall
|
||
test/acts_as_yaffle_test.rb:10:in `test_a_wickwalls_yaffle_text_field_should_be_last_tweet'
|
||
|
||
5 tests, 3 assertions, 0 failures, 2 errors, 0 skips
|
||
```
|
||
|
||
This tells us that we don't have the necessary models (Hickwall and Wickwall) that we are trying to test.
|
||
We can easily generate these models in our "dummy" Rails application by running the following commands from the
|
||
test/dummy directory:
|
||
|
||
```bash
|
||
$ cd test/dummy
|
||
$ rails generate model Hickwall last_squawk:string
|
||
$ rails generate model Wickwall last_squawk:string last_tweet:string
|
||
```
|
||
|
||
Now you can create the necessary database tables in your testing database by navigating to your dummy app
|
||
and migrating the database. First
|
||
|
||
```bash
|
||
$ cd test/dummy
|
||
$ rake db:migrate
|
||
$ rake db:test:prepare
|
||
```
|
||
|
||
While you are here, change the Hickwall and Wickwall models so that they know that they are supposed to act
|
||
like yaffles.
|
||
|
||
```ruby
|
||
# test/dummy/app/models/hickwall.rb
|
||
|
||
class Hickwall < ActiveRecord::Base
|
||
acts_as_yaffle
|
||
end
|
||
|
||
# test/dummy/app/models/wickwall.rb
|
||
|
||
class Wickwall < ActiveRecord::Base
|
||
acts_as_yaffle yaffle_text_field: :last_tweet
|
||
end
|
||
|
||
```
|
||
|
||
We will also add code to define the acts_as_yaffle method.
|
||
|
||
```ruby
|
||
# yaffle/lib/yaffle/acts_as_yaffle.rb
|
||
module Yaffle
|
||
module ActsAsYaffle
|
||
extend ActiveSupport::Concern
|
||
|
||
included do
|
||
end
|
||
|
||
module ClassMethods
|
||
def acts_as_yaffle(options = {})
|
||
# your code will go here
|
||
end
|
||
end
|
||
end
|
||
end
|
||
|
||
ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle
|
||
```
|
||
|
||
You can then return to the root directory (`cd ../..`) of your plugin and rerun the tests using `rake`.
|
||
|
||
```
|
||
1) Error:
|
||
test_a_hickwalls_yaffle_text_field_should_be_last_squawk(ActsAsYaffleTest):
|
||
NoMethodError: undefined method `yaffle_text_field' for #<Class:0x000001016661b8>
|
||
/Users/xxx/.rvm/gems/ruby-1.9.2-p136@xxx/gems/activerecord-3.0.3/lib/active_record/base.rb:1008:in `method_missing'
|
||
test/acts_as_yaffle_test.rb:5:in `test_a_hickwalls_yaffle_text_field_should_be_last_squawk'
|
||
|
||
2) Error:
|
||
test_a_wickwalls_yaffle_text_field_should_be_last_tweet(ActsAsYaffleTest):
|
||
NoMethodError: undefined method `yaffle_text_field' for #<Class:0x00000101653748>
|
||
Users/xxx/.rvm/gems/ruby-1.9.2-p136@xxx/gems/activerecord-3.0.3/lib/active_record/base.rb:1008:in `method_missing'
|
||
test/acts_as_yaffle_test.rb:9:in `test_a_wickwalls_yaffle_text_field_should_be_last_tweet'
|
||
|
||
5 tests, 3 assertions, 0 failures, 2 errors, 0 skips
|
||
|
||
```
|
||
|
||
Getting closer... Now we will implement the code of the acts_as_yaffle method to make the tests pass.
|
||
|
||
```ruby
|
||
# yaffle/lib/yaffle/acts_as_yaffle.rb
|
||
|
||
module Yaffle
|
||
module ActsAsYaffle
|
||
extend ActiveSupport::Concern
|
||
|
||
included do
|
||
end
|
||
|
||
module ClassMethods
|
||
def acts_as_yaffle(options = {})
|
||
cattr_accessor :yaffle_text_field
|
||
self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
|
||
end
|
||
end
|
||
end
|
||
end
|
||
|
||
ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle
|
||
```
|
||
|
||
When you run `rake` you should see the tests all pass:
|
||
|
||
```bash
|
||
5 tests, 5 assertions, 0 failures, 0 errors, 0 skips
|
||
```
|
||
|
||
### Add an Instance Method
|
||
|
||
This plugin will add a method named 'squawk' to any Active Record object that calls 'acts_as_yaffle'. The 'squawk'
|
||
method will simply set the value of one of the fields in the database.
|
||
|
||
To start out, write a failing test that shows the behavior you'd like:
|
||
|
||
```ruby
|
||
# yaffle/test/acts_as_yaffle_test.rb
|
||
require 'test_helper'
|
||
|
||
class ActsAsYaffleTest < Test::Unit::TestCase
|
||
|
||
def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
|
||
assert_equal "last_squawk", Hickwall.yaffle_text_field
|
||
end
|
||
|
||
def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
|
||
assert_equal "last_tweet", Wickwall.yaffle_text_field
|
||
end
|
||
|
||
def test_hickwalls_squawk_should_populate_last_squawk
|
||
hickwall = Hickwall.new
|
||
hickwall.squawk("Hello World")
|
||
assert_equal "squawk! Hello World", hickwall.last_squawk
|
||
end
|
||
|
||
def test_wickwalls_squawk_should_populate_last_tweet
|
||
wickwall = Wickwall.new
|
||
wickwall.squawk("Hello World")
|
||
assert_equal "squawk! Hello World", wickwall.last_tweet
|
||
end
|
||
end
|
||
```
|
||
|
||
Run the test to make sure the last two tests fail with an error that contains "NoMethodError: undefined method `squawk'",
|
||
then update 'acts_as_yaffle.rb' to look like this:
|
||
|
||
```ruby
|
||
# yaffle/lib/yaffle/acts_as_yaffle.rb
|
||
|
||
module Yaffle
|
||
module ActsAsYaffle
|
||
extend ActiveSupport::Concern
|
||
|
||
included do
|
||
end
|
||
|
||
module ClassMethods
|
||
def acts_as_yaffle(options = {})
|
||
cattr_accessor :yaffle_text_field
|
||
self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
|
||
|
||
include Yaffle::ActsAsYaffle::LocalInstanceMethods
|
||
end
|
||
end
|
||
|
||
module LocalInstanceMethods
|
||
def squawk(string)
|
||
write_attribute(self.class.yaffle_text_field, string.to_squawk)
|
||
end
|
||
end
|
||
end
|
||
end
|
||
|
||
ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle
|
||
```
|
||
|
||
Run `rake` one final time and you should see:
|
||
|
||
```
|
||
7 tests, 7 assertions, 0 failures, 0 errors, 0 skips
|
||
```
|
||
|
||
NOTE: The use of `write_attribute` to write to the field in model is just one example of how a plugin can interact with the model, and will not always be the right method to use. For example, you could also use `send("#{self.class.yaffle_text_field}=", string.to_squawk)`.
|
||
|
||
Generators
|
||
----------
|
||
|
||
Generators can be included in your gem simply by creating them in a lib/generators directory of your plugin. More information about
|
||
the creation of generators can be found in the [Generators Guide](generators.html)
|
||
|
||
Publishing your Gem
|
||
-------------------
|
||
|
||
Gem plugins currently in development can easily be shared from any Git repository. To share the Yaffle gem with others, simply
|
||
commit the code to a Git repository (like GitHub) and add a line to the Gemfile of the application in question:
|
||
|
||
```ruby
|
||
gem 'yaffle', git: 'git://github.com/yaffle_watcher/yaffle.git'
|
||
```
|
||
|
||
After running `bundle install`, your gem functionality will be available to the application.
|
||
|
||
When the gem is ready to be shared as a formal release, it can be published to [RubyGems](http://www.rubygems.org).
|
||
For more information about publishing gems to RubyGems, see: [Creating and Publishing Your First Ruby Gem](http://blog.thepete.net/2010/11/creating-and-publishing-your-first-ruby.html)
|
||
|
||
RDoc Documentation
|
||
------------------
|
||
|
||
Once your plugin is stable and you are ready to deploy do everyone else a favor and document it! Luckily, writing documentation for your plugin is easy.
|
||
|
||
The first step is to update the README file with detailed information about how to use your plugin. A few key things to include are:
|
||
|
||
* Your name
|
||
* How to install
|
||
* How to add the functionality to the app (several examples of common use cases)
|
||
* Warnings, gotchas or tips that might help users and save them time
|
||
|
||
Once your README is solid, go through and add rdoc comments to all of the methods that developers will use. It's also customary to add '#:nodoc:' comments to those parts of the code that are not included in the public API.
|
||
|
||
Once your comments are good to go, navigate to your plugin directory and run:
|
||
|
||
```bash
|
||
$ rake rdoc
|
||
```
|
||
|
||
### References
|
||
|
||
* [Developing a RubyGem using Bundler](https://github.com/radar/guides/blob/master/gem-development.md)
|
||
* [Using .gemspecs as Intended](http://yehudakatz.com/2010/04/02/using-gemspecs-as-intended/)
|
||
* [Gemspec Reference](http://docs.rubygems.org/read/chapter/20)
|
||
* [GemPlugins: A Brief Introduction to the Future of Rails Plugins](http://www.intridea.com/blog/2008/6/11/gemplugins-a-brief-introduction-to-the-future-of-rails-plugins)
|